The invention described and claimed in this application relates to granular filters and, more particularly, to continuously regenerate granular filters operatable at high temperature and pressure which are particularly suited for cleaning gas used to operate a gas turbine.
With the current shortage of many fuels which have traditionally been used to generate heat and power, electric generating plants using coal with high impurity and ash levels and other solid fuels are playing an ever-increasing role in supplying electric power. Other solid fuels may include, for example, combustible solid wastes such as trash, rubbish, garbage, agricultural residues, and industrial residues. It has been found that gas streams formed by burning such fuels contain a relatively high concentration of fine particles matter which must be removed in order for the system to operate efficiently and effectively. Of particular importance, is a system utilizing a turbine generator in which the hot pressurized gas can be cleaned without significantly lowering the temperature or pressure of the gas.
Different types of filters or separators have been tried, but many have significant drawbacks which prevent them from being used. For example, inertial separators such as cyclones have been found not to be effective in removing micron or sub-micron size particles and since cyclones operate at a relatively high velocity, e.g. 50-150 feet/second, if the particulate material has a tendency to stick to surfaces dense deposits in the cyclone result.
Bag houses, where the gas is channeled through a finely meshed material to filter out the particulate material, are limited to relatively low temperatures because of the material used to form the bag. In addition, bag houses are not effective at velocities greater than 15 feet/min., which would require an excessively large filter area at great cost.
Electrostatic precipitators have found not to be effective because of their relatively large size and complex construction. In addition, electrostatic precipitators consume relatively high amounts of power and are sensitive to electrical properties of the particulate material to be removed from the gas. Although electrostatic precipitators have a relatively high maximum collection efficiency, the overall collection efficiency is not as great because of uneven gas flow distribution and particulate re-entrainment when the plates are cleaned.
It has been found that filters using a granular material as a filter medium offer significant advantages for use in a high temperature and pressure environment where high efficiency cleaning is necessary. However, no granular filters were known which operated continuously and efficiently for long periods of time under such conditions of high pressure and temperature.